1. Field of the Invention
This invention relates to the partial oxidation and/or reforming of hydrocarbons, and more particularly to the production of hydrogen and carbon monoxide by the partial oxidation of hydrocarbons, steam reforming of hydrocarbons or a combination of the two to achieve an auto-thermal process. Specifically, the invention relates to the use of an oxygen ion conducting ceramic in particulate form in a cyclic process, involving the reaction of oxygen in air feed with the ceramic in one step and the reaction of hydrocarbon feed, with or without steam, with the above oxygen-enriched ceramic in another step, to produce hydrogen and carbon monoxide products.
2. Description of Art
Synthesis gas and its components, hydrogen and carbon monoxide, are conventionally produced by the steam methane reforming (SMR) or by the high temperature partial oxidation of hydrocarbons with controlled amounts of air or oxygen. In the SMR process, a large amount of heat must be supplied into the reactor for sustaining the highly endothermic SMR reaction. Therefore, expensive shell-and-tube type reactors must be used to facilitate the heat exchange. The overall production rate of the SMR process is often limited by the heat transfer rate from the shell side to the tube side where the reaction is taking place. In the partial oxidation process, the overall reaction is exothermic, therefore it does not require an external heat supply. However, it does require the use of an oxidant, such as air or oxygen. Although air is less expensive and more convenient to use in partial oxidation reactions, it is less attractive than oxygen because the large quantities of nitrogen that are produced when air is used as the oxidant must be subsequently separated from the product gas prior to its use. The cost of gas separation and purification equipment required to purify the product gas adds considerably to the cost of synthesis gas production using air.
U.S. Pat. No. 5,149,516 to Han et al., discloses a process for the partial oxidation of methane over a perovskite catalyst to produce carbon monoxide and hydrogen. The process involves contacting a source of methane and a source of oxygen together with a perovskite catalyst. The perovskite acts as a catalyst in the reaction of methane and oxygen in a continuous process, i.e. the perovskite does not participate in the reaction, but promotes the reaction rate. In this process, if air is used as the oxygen source, the products (hydrogen and carbon monoxide) will be contaminated with a large amount of nitrogen.
Although oxygen is more desirable than air as an oxidant for partial oxidation reactions, its use involves certain disadvantages. The oxygen must be imported into the system, or it must be generated on site, for example, by means of a cryogenic air separation plant or other means, such as a membrane or a Pressure Swing Adsorption (PSA) system. In either alternative, using oxygen as the oxidant likewise adds considerably to the cost of the process.
More economical methods of on site production of oxygen for applications such as hydrocarbon partial oxidation reactions are continuously sought. U.S. Pat. No. 5,755,840 to Beer discloses a process for providing oxygen to a feed gas, wherein the oxygen is first absorbed from an oxygen-containing gas (e.g., air) by passing the air over an oxygen-sorbent material (e.g., a solid-state lithium cyanocobaltate) until the sorbent material is substantially saturated after which the feed gas (e.g. natural gas) is passed in contact with the sorbent material to desorb the oxygen into the feed gas. This process produces a gaseous mixture of oxygen and natural gas, which will require additional equipment and means to make hydrogen and carbon monoxide products, such as reactors, catalyst and means for heating up the mixture. The sorbent material, such as lithium cyanocobaltate can only adsorb oxygen on its surface at temperatures lower than 100xc2x0 C.; the lower the temperature, the higher the amount adsorbed.
U.S. Pat. No. 5,714,091 discloses an oxygen-based hydrocarbon partial oxidation process in which the oxygen is produced on site by subjecting air to membrane separation using a membrane constructed of oxygen ion conducting ceramic material. Oxygen, which is permeable to the membrane, passes through the membrane and is made to react with hydrocarbons on the downstream side of the membrane unit. The disadvantages of this method of oxygen production are the high cost of fabrication of the membrane and the difficulty of producing membrane structures that are leak-proof.
The present invention provides a system and process for the partial oxidation of hydrocarbons, steam reforming of hydrocarbons, or a combination of the two to achieve an auto-thermal process in which oxygen is supplied into the reaction from an oxygen-containing gas using a relatively inexpensive particulate oxygen ion conducting ceramic and a simple reactor design. The inventive process is cyclic, wherein oxygen containing gas and hydrocarbon are fed into the reactor in separate steps. In one step, the oxygen ion conducting ceramic selectively reacts with molecular oxygen at high temperatures by dissociating gas phase oxygen molecules into oxygen ions at its surface and then incorporating these ions into its lattice structure by means of ion conduction through the oxygen vacancies in its lattice structure. This results in the formation of an oxygen-enriched ceramic. In another step, the oxygen-enriched ceramic reacts with hydrocarbon feed to form a product containing hydrogen and carbon monoxide. The process of this invention has several advantages, namely: (1) the separation of oxygen from oxygen-containing gas is conducted in the same vessel as that used for the partial oxidation of hydrocarbons; (2) there is no oxygen in the gas phase during the partial oxidation of hydrocarbons, providing a much safer operating environment; and (3) oxygen ion conducting ceramic in a particulate form is easier to fabricate and costs much less than one in a membrane form. In addition, the process has the advantage that the heat produced during the step in which oxygen reacts with the oxygen ion conducting ceramic can be used to increase the overall efficiency of the process by maintaining the ceramic at the desired temperature without an external heat source and it can also be used to preheat incoming feed streams, by way of heat exchange means.
According to a broad embodiment, the invention includes a process for producing hydrogen and carbon monoxide by the partial oxidation of at least one hydrocarbon comprising the steps of:
(a) contacting an oxygen ion conducting ceramic in particulate form in a reactor with an oxygen-containing gas at a temperature in the range between about 300 and 1400xc2x0 C. and at a pressure in the range between about 1 and 50 bara, wherein oxygen from the oxygen-containing gas is reacted with the ceramic, thereby producing an oxygen-enriched ceramic; and
(b) contacting the oxygen-enriched ceramic in the reactor with a hydrocarbon at a temperature in the range between about 300 and 1400xc2x0 C., thereby producing a product gas through the reaction between the oxygen-enriched ceramic and the hydrocarbon;
wherein step (b) is conducted at a pressure of between about 1 and 50 bara.
Another embodiment of the present invention includes a process for the continuous production of hydrogen and carbon monoxide by the partial oxidation of at least one hydrocarbon, using two reactors, comprising the steps of:
(a) in a first reactor, contacting a first oxygen ion conducting ceramic with an oxygen-containing gas at a temperature in the range between about 300 and 1400xc2x0 C. and at a pressure in the range between about 1 and 50 bara, wherein oxygen from the oxygen-containing gas reacts with the first ceramic, thereby producing a first oxygen-enriched ceramic; and contacting the first oxygen-enriched ceramic with the hydrocarbon at a temperature in the range between about 300 and 1400xc2x0 C., thereby producing a first product gas; and
(b) in a second reactor, contacting a second oxygen ion conducting ceramic with an oxygen-containing gas at a temperature in the range between about 300 and 1400xc2x0 C. and at a pressure in the range between about 1 and 50 bara, wherein oxygen from the oxygen-containing gas reacts with the second ceramic, thereby producing a second oxygen-enriched ceramic; and contacting the second oxygen-enriched ceramic with the hydrocarbon at a temperature in the range between about 300 and 1400xc2x0 C., thereby producing a second product gas.
The continuous production process may be operated wherein the first reactor is 180xc2x0 out of phase with the second reactor, whereby either:
(a) the first product gas is being formed in and removed from the first reactor while the oxygen from oxygen-containing gas is reacting with the second ceramic in the second reactor; or
(b) oxygen from oxygen-containing gas is reacting with the first ceramic in the first reactor while the second product gas is being formed in and removed from the second reactor.
Continuous production can be achieved by using two or more reactors operated in parallel. The number of reactors is a matter of selection; the number of reactors and the operating sequence can be selected to optimize the continuous production of hydrogen and carbon monoxide. With multiple reactors the operating sequence will need to be modified to achieve the desired productivity and to maintain all the reactors in thermal balance. This is accomplished by generally known methods used in practice.
In another embodiment, the present invention includes a system for the continuous production of a product gas from the partial oxidation of at least one hydrocarbon, the system comprising:
(a) a first reactor comprising a first oxygen ion conducting ceramic;
(b) means for contacting the first oxygen ion conducting ceramic with an oxygen-containing gas at a temperature in the range between about 300 and 1400xc2x0 C. and at a pressure in the range between about 1 and 50 bara, wherein oxygen from the oxygen-containing gas reacts with the first ceramic, thereby producing a first oxygen-enriched ceramic;
(c) means for contacting the first oxygen-enriched ceramic with the hydrocarbon at a temperature in the range between about 300 and 1400xc2x0 C., thereby producing a first product gas;
(d) a second reactor comprising a second oxygen ion conducting ceramic;
(e) means for contacting the second oxygen ion conducting ceramic with an oxygen-containing gas at a temperature in the range between about 300 and 1400xc2x0 C. and at a pressure in the range between about 1 and 50 bara, wherein oxygen from the oxygen-containing gas reacts with the second ceramic, thereby producing a second oxygen-enriched ceramic; and
(f) means for contacting the second oxygen-enriched ceramic with the hydrocarbon at a temperature in the range between about 300 and 1400xc2x0 C., thereby producing a second product gas.
The system of the present invention may further comprise a first means for removing the first product gas from the first reactor and a second means for removing the second product gas from the second reactor, wherein the first and second removing means can be either different or the same.
In another preferred embodiment, the system includes at least one means, such as a heat exchanger, for heating the oxygen-containing gas, the hydrocarbon gas, and combinations thereof.
The process of the present invention can be used to produce product gases other than synthesis gas by disposing or mixing a catalyst with the oxygen ion conducting ceramic.
In one embodiment of the present invention there is included a process for the production of cyclic anhydrides via partial oxidation of at least one hydrocarbon comprising the steps of:
(a) contacting an oxygen ion conducting ceramic having an anhydride-forming catalyst disposed thereon with an oxygen-containing gas at a temperature in the range between about 250 and 650xc2x0 C. and at a pressure in the range between about 1 and 50 bara, wherein oxygen from the oxygen-containing gas reacts with the ceramic, thereby producing an oxygen-enriched ceramic; and
(b) contacting the oxygen-enriched ceramic with hydrocarbon at a temperature in the range between about 250 and 650xc2x0 C., thereby producing cyclic anhydrides.
In a preferred embodiment of the process to produce cyclic anhydrides, the anhydride-forming catalyst is a vanadium-based catalyst.
In another embodiment of the present invention, there is included a process for the production of alkylene oxides via partial oxidation of at least one hydrocarbon comprising the steps of:
(a) contacting an oxygen ion conducting ceramic having an alkylene-forming catalyst disposed thereon with an oxygen-containing gas at a temperature in the range between about 250 and 650xc2x0 C. and at a pressure in the range between about 1 and 50 bara, wherein oxygen from the oxygen-containing gas reacts with the oxygen ion conducting ceramic, thereby producing an oxygen-enriched ceramic; and
(b) contacting the oxygen-enriched ceramic with hydrocarbon at a temperature in the range between about 250 and 650xc2x0 C., thereby producing alkylene oxides.
In a preferred embodiment of the process to produce alkylene oxides, the alkylene-forming catalyst is a silver oxide catalyst.
In another embodiment of the present invention, there is included a process for the production of chlorinated hydrocarbons via partial oxidation of at least one hydrocarbon comprising the steps of:
(a) contacting an oxygen ion conducting ceramic having a chlorinated hydrocarbon-forming catalyst disposed thereon with an oxygen-containing gas at a temperature in the range between about 250 and 650xc2x0 C. and at a pressure in the range between about 1 and 50 bara, wherein oxygen from the oxygen-containing gas reacts with the oxygen ion conducting ceramic, thereby producing an oxygen-enriched ceramic; and
(b) contacting the oxygen-enriched ceramic with hydrocarbon at a temperature in the range between about 250 and 650xc2x0 C., thereby producing chlorinated hydrocarbons.
In a preferred embodiment of the process to produce chlorinated hydrocarbons, the chlorinated hydrocarbon-forming catalyst is a copper chloride catalyst.
In another embodiment of the present invention, there is included a process for the production of aldehydes via partial oxidation of at least one hydrocarbon comprising the steps of:
(a) contacting an oxygen ion conducting ceramic having an aldehyde-forming catalyst disposed thereon with an oxygen-containing gas at a temperature in the range between about 250 and 650xc2x0 C. and at a pressure in the range between about 1 and 50 bara, wherein oxygen from the oxygen-containing gas reacts with the oxygen ion conducting ceramic, thereby producing an oxygen-enriched ceramic; and
(b) contacting the oxygen-enriched ceramic with hydrocarbon at a temperature in the range between about 250 and 650xc2x0 C., thereby producing aldehydes.
In a preferred embodiment of the process to produce aldehydes, the aldehyde-forming catalyst is a catalyst selected from the group consisting of: copper chloride, palladium chloride, molybdenum, bismuth, iron, and mixtures thereof.
In another embodiment of the present invention, there is included a process for the production of olefinically unsaturated nitriles via partial oxidation of at least one hydrocarbon comprising the steps of:
(a) contacting an oxygen ion conducting ceramic having a nitrile-forming catalyst disposed thereon with an oxygen-containing gas at a temperature in the range between about 250 and 650xc2x0 C. and at a pressure in the range between about 1 and 50 bara, wherein oxygen from the oxygen-containing gas reacts with the oxygen ion conducting ceramic, thereby producing an oxygen-enriched ceramic; and
(b) contacting the oxygen-enriched ceramic with hydrocarbon at a temperature in the range between about 250 and 650xc2x0 C., thereby producing olefinically unsaturated nitrites.
In a preferred embodiment of the process to produce olefinically unsaturated nitrites, the nitrile-forming catalyst is a catalyst selected from the group consisting of: bismuth-molybdenum oxide catalyst and iron-antimony oxide catalyst.